Colabtools: [Bug] print(..., end="\r") doesn't produce any output

[Androbin]

None of the following produce any output:

• print(..., end="\r")
• print(..., end="\r", flush=True)
• print(..., end="\r") directly followed by sys.stdout.flush()

not even after the cell has finished execution.
Meaning, it's not an issue with the buffering simply delaying the output.

[blois]

Carriage returns are automatically clearing any contents back to the newline, regardless of what follows.

Is there a specific scenario in which more advanced handling is desired?

[Androbin]

Carriage returns don't (normally) directly override the last line.
Subsequent text will overwrite the already printed text (or parts of it).
At least with forced flushing, it should print some-thing.

The common use case is to continuously print the state of the program:

print("initializing", end="\r")
# ...
print("fetching data", end="\r")
# ...
for train_step in range(1000):
  # ...
  print("training | step:", train_step, "| loss:", loss, end="\r")
# ...
print("accuracy", accuracy)

This way, you don't spam the notebook output with pages of redundant logging.

[blois]

Two examples of approaches for doing this:
https://colab.research.google.com/gist/blois/81711a73150e4fa1773782068fbb69ec/clearing-outputs.ipynb

[Androbin]

Thanks! Good to know.

But I just noticed that !pip install seems to have trouble printing:
Running setup.py bdist_wheel for atari-py ... - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | / - \ | done
It's supposed to animate the last symbol between - \ | / in place.

[blois]

We fixed an issue with this about a week ago and I have no longer observed the issue during !pip install.

A simple repro of it working is:
https://colab.research.google.com/gist/blois/d8e4ae3df9eef1a8a99245403024883b/spinner.ipynb

If you happen to have an example of containing the final result then we can take a look at it.

[Androbin]

I am able to reproduce with these three lines:

!apt-get install cmake
!pip install gym
!pip install gym[atari]

[blois]

The fix will be rolling out in a few days, thank you for the report!

[JSTHoffman]

This is an old issue, but I've found that using end='' with a carriage return at the beginning of a string produces the desired effect—overwriting the previous line—and is much simpler than the solutions linked above.

i.e. print('\ryour text here', end='')